From the Director





by Rex Parker, Phd

From Stone to Star. The relationship of stars to common earthly things is closer than one might think. Advances in astrophysics over the past century have revised the story of geology by providing a detailed explanation for how minerals found on earth were created in stars. That process, called stellar nucleosynthesis, was elegantly described to AAAP members at a lecture last fall by Dr Jack Hughes of Rutgers Astronomy Dept. Nuclear fusion in stars is understood to create all the chemical elements up to atomic mass of iron (Fe, atomic number 26). But heavier nuclei cannot be generated at the observed abundances in the universe under the conditions within stars. Rather they are produced through much more energetic and cataclysmic processes, chief among these being supernova explosions. Over time this has seeded the interstellar spaces with vast clouds of particles and gases that are the stuff from which new planetary systems form. Although the 66 natural elements (all found on earth) heavier than Fe make up less than 0.1% of the total mass of the universe, they’re essential to biological life and human society.

Back down on earth, I’ve recently had a close encounter with the great diversity of minerals found in the top layer of our planet. Over the past couple months I’ve moved the family rock and mineral collection to our home in New Jersey. Imagining the processes that created the beautiful and highly variable crystalline rocks and colorful blends of agates and jaspers is a mind-expanding exercise. When touching a nodule of turquoise the realization that the origin lies in stars and supernovae brings home the reality of what astrophysics means to geology, chemistry, and biology. Can’t help but think of Carl Sagan’s words about us being star stuff. When looking through a telescope at emission nebula and “HII regions” where new stars are being born in the deep sky, consider that these precious minerals are being formed right there.

For a good book on the topic, I recommend “From Stone to Star” by Claude Allegre. And keep an eye out for emerging ideas about the formation of the heavier elements. Supernovae are not the only explanation, as their frequency across the universe does not appear to equate with the observed abundances of elements such as gold and platinum. One recent hypothesis is that neutron star collisions can also generate heavier elements. Of course neutron stars are the gravitationally collapsed core products of supernovae, so the latter are not being disrespected by the neutron star hypothesis. The recent breakthrough observation by LIGO in 2017 of gravitational waves, interpreted as being generated by a neutron star merger, has supported this proposal. It has been estimated that the “kilonova” gravitational wave event detected by LIGO (termed GW170917) generated about 10 earth masses equivalent of the element gold!

The AAAP Washington Crossing Observatory is for all club members. As the main hub for observational astronomy, member gatherings, and public outreach, the Observatory is central to the club’s mission. You don’t need to be an expert, just come out on Friday public nights starting April 5 through Nov 1. If you have thought learning more about telescope hardware, software, and technical aspects, I urge you to come out to see what’s up there through the AAAP’s telescopes (see list of equipment below). If you’d like to enter the training program to become qualified to access the observatory 24/7, please contact me or send an e-mail note to

Telescope equipment for member use at the AAAP Observatory as of April 2019.

  • Paramount-ME #1, robotic equatorial mount
    • Mount run with TheSkyX planetarium and control software under Win10 computer.
    • Celestron-14 Schmidt-Cassegrain telescope, D=355mm (14-inch), f/11, FL=3900mm.
    • New Stellarview 80 mm right-angle finder scope on the C-14.
    • Explore Scientific ED127 refractor telescope, D=127mm (5-inch), f/7.5, FL=950 mm, triplet air-spaced apochromatic refractor.
    • Numerous 2-inch and 1-1/4-inch eyepieces for these telescopes.
    • Starlight Xpress Ultrastar Colour CCD camera.
    • Starlight Live and SharpCap software cameras.
    • Verizon FiOS is available inside the Observatory.
  • Paramount-ME #2, robotic equatorial mount
    • Mount run with TheSkyX planetarium and control software under Win10 computer.
    • Hastings-Byrne 61/4-inch refractor, f/14.6, FL=2310mm. This fine historic instrument is a great planetary telescope, dating to 1879 with the original air-spaced doublet lens and steel tube intact.
    • Takahashi Mewlon-250, D=250mm (10-inch) Dall-Kirkham reflector telescope, with -inch TMB Optical dielectric-diagonal and Feathertouch 2-inch Crayford focuser.
    • Numerous 2-inch and 1-1/4-inch eyepieces including Panoptic 27 mm and 41 mm for the M250.
    • ZWO ASI 294 Pro color CMOS camera
    • Starlight Live and SharpCap software set up for EAA cameras

Posted in April 2019, Sidereal Times | Tagged , | Leave a comment

From the Program Chair

by Ira Polans

The April meeting of the AAAP will be held on the 9th at 7:30PM in the auditorium (Room 145) of Peyton Hall on the Princeton University campus.

The featured talk is by Gino Segre and Bettina Hoerlin on their book THE POPE OF PHYSICS: Enrico Fermi and the Birth of the Atomic Age. Enrico Fermi is unquestionably the most famous scientist to come from Italy since Galileo, so revered by his peers that he was known as “the Pope,” because his scientific instincts and skills were to be “infallible.” A physics Nobel Prize winner in 1938, he was one of the most productive and creative scientists of the twentieth century. His work changed our world. The largest particle accelerator in the United States, the nation’s most significant presidential award in science and technology, and the element fermium all bear his name.

This major biography of a towering figure in the history of science portrays Fermi as an architect of the atomic age with all its complexities. In THE POPE OF PHYSICS: Enrico Fermi and the Birth of the Atomic Age Gino Segrè and Bettina Hoerlin bring this scientific visionary to life. From his modest beginnings in Rome amidst the tumultuous environment of fascist Italy, to his immigration to America escaping anti-Semitism, he became a key figure in the Manhattan Project. His work under the football field of the University of Chicago on the world’s first nuclear chain reaction was critical in subsequently building the atomic bomb. THE POPE OF PHYSICS delves into the personal and scientific life of Fermi and how political and social forces shaped the man, and how he, in turn, shaped them. A thrilling history of scientific innovation in the twentieth century—including the controversial issue of nuclear weapons—this is the comprehensive biography that Fermi deserves. During the break there will be a book signing.

The 10 minute talk will be given by Dave and Jen Skitt and Ira Polans about our trip last summer to Chicago and the Yerkes Observatory.

There will be a meet-the-speaker at 6 PM at Winberie’s in Palmer Square. If you want to join us for dinner please email me at by Noon on April 9.

Looking forward to you joining us at the April meeting!

Posted in April 2019, Sidereal Times | Tagged , | Leave a comment

Outreach Blotter

by Gene Allen, Outreach Chair

David Letcher, our former, longtime Outreach Chair, served as Event Lead for an Outreach Event in Hopewell on March 22. His report on the Event is as follows:

“Well, we continued our tradition of giving a star party at Hopewell Elementary School tonight, a tradition that began through the efforts of our late member Gene Ramsey.

Victor Davis and I went to the school tonight with 100% overcast skies with occasional rain and very windy conditions BUT Victor Davis saved the night!

Victor (with my humble assistance) brought his 3 inch Questar and assorted equipment from his car into the school auditorium and, under Victor’s direction, we set up a neat alternative to observing the real night sky. To wit, Victor, who had purchased a bunch of 35 mm slides of astronomical objects from the Astronomical Society of the Pacific, set up an arrangement in which children could look through his eyepiece and see a slide’s object, such as a star cluster, just as if they were outside!

We were also happy to attend a one-hour demonstration of gas laws by a scientist who owns a business of doing science lectures/demos to school groups. That was good fun!

It was a good time had by all!”

We have a number of Outreach Events coming up, from a Scout Troop at the opening night at Simpson Observatory to Communiversity Day April 28 to more than a half dozen library presentations over the summer. We are working on developing a somewhat “canned” presentation that can be adapted to daytime or evening events for a wide age range. My wish is to come up with something that can be offered by any of our Outreach volunteers with little additional preparation. If any of our membership has any material or assistance to offer toward this effort, please get in touch with me.

Posted in April 2019, Sidereal Times | Tagged , | Leave a comment

March 2019 meeting minutes

by Jim Poinsett, Secretary

Minutes of the March 2019 Meeting of the Amateur Astronomers Association of Princeton

  • Rex opened the meeting and welcomed our new members. He then introduced Ira, the Program Chair.
  • Ira introduced the evening’s speaker Dr. Scott Tremaine and his talk on Pluto, Sedna, Planet X, the Oort cloud, and Oumuamua: a report on the outer fringes of the solar system.
  • After the lecture Rex called the meeting to order at 9:00 PM.
  • The United Nations has designated 2019 the year of the Periodic Table of the Elements.
  • Rex Parker show a clip of an asteroid he inadvertently captured while photographing another object.
  • Observatory report
    • Dave presented keys to the new keyholders
    • An estimate for tree removal has been obtained and will be presented to the park supervisor. Some diseased elm trees have already been removed by the park. There are six trees that remain that we would like removed, three are dead or nearly dead.
    • Public nights begin April 5th with Team 3, you should have received the complete roster and schedule by now.
  • Communiversity will be held on the last Sunday in April on the 28th. Let Larry Kane know if you will be able to attend.
  • Check the website for future events.
  • NEAF is being held on April 6th and 7th.
  • There is an opportunity to attend a Celestial Navigation class to be held in Princeton. There are two options, easy and modern. The class will be held on 2 consecutive days, 8 hours each day. Cost will depend on number of attendees, approximately $100 to $200 per person.
  • There are two sessions planned for a Planetarium session followed by an Observatory session. They are May 3rd and 10th. Extra members may be needed at the observatory to assist and extra telescopes are always welcome.
  • There will be a picnic at the NJ State Museum and Planetarium on the afternoon and evening of July 20th to celebrate the 50th anniversary of the Apollo 11 moon landing, there will also be a new exhibit opening in May at the NJ State Museum all about space and the moon landing.
  • There being no new business the meeting was adjourned.
Posted in April 2019, Sidereal Times | Tagged , | Leave a comment

The Earth as a Peppercorn

by Victor Davis

The Earth as a Peppercorn

Seeking a “Gee Whiz” Moment
With spring comes an upwelling in our club’s outreach activities, from Friday night star parties at the observatory to on-site presentations at schools, libraries, and other venues. How can we make these encounters memorable to a public accustomed to experiencing the cosmos superficially? How can we provide experiences like the ones that got us hooked on astronomy lo, those many years ago? Certainly a firstlook at Saturn through a telescope eyepiece qualifies as a transcendental experience. Or a look at the detail-rich Moon or solar prominences or (per David Zahler) “original photons” from a faraway galaxy. With experience, the list grows. Getting an “OMG” from a grownup or a “Sick!” from a younger visitor feels pretty good.

An Outdoor Nature Activity
Sky and Telescope describes amateur astronomy as an “outdoor nature activity,” and my favorite outreach activities exemplify that view. So, here’s a hands on activity that I heartily recommend as an introduction to astronomy for people of all ages. It’s a perspective-altering exercise that helps to visualize the sizes of astronomical objects—and the spaces between them—beginning with the Solar System. This solar system model, or planet walk, or cosmic hike was developed by Guy Ottewell and published as “The Thousand Yard Model.” I have added a few refinements of my own, and indeed, the level of appropriate detail to convey will vary depending on the interest level and sophistication of the hikers. Ottewell points out that there’s a big difference between knowing something and apprehending it, and so reading this description of the planet walk will not substitute for performing it. It will not fail to impress even the most jaded participant.

A Matter of Scale
Science writers often try to incorporate a sense of scale in their descriptions. Books sometimes contain fold-out illustrations of the planets to scale. Often the Sun is represented as an arc segment that runs off the edge of the page. Rarely are the spaces between them shown to the same scale. Then, there is the challenge of choosing a convenient and pedagogically effective scale. Ottewell suggests a scale of 1:6,336,000,000, or one inch equals one hundred thousand miles. On this scale, the Sun, a star roughly 864,000 miles in diameter, is represented by a ball approximately 8.64 inches wide—almost exactly the size of a regulation soccer ball. On this same scale, model Mercury’s diameter is 0.03 inch and represented by a pinhead. Venus and Earth, similar-sized planets with scale-model diameters of about 0.08 inch, are represented by—you guessed it—peppercorns. The table summarizes the scale-model objects and distances:

Solar System Object Scale Model Size Represented by Incremental distance
Sun 8.64 inches Soccer ball
Mercury 0.03 inches Pinhead 10 paces
Venus 0.08 inches Peppercorn 9 paces
Earth 0.08 inches Peppercorn 7 paces
Moon 0.02 inches Pinhead 2.4 inches
Mars 0.04 inches Pinhead 14 paces
Jupiter 0.9 inches Pecan 95 paces
Saturn 0.7 inches Hazelnut 112 paces
Uranus 0.3 inches Pistachio 249 paces
Neptune 0.3 inches Pistachio 281 paces
Pluto 0.02 inches Pinhead 242 paces

The choice of representative objects is somewhat arbitrary, and the dimensions are inexact. It does not matter that they are not particularly spherical. What matters is that they are common objects the learner associates with a rough size. A pecan conjures up a lasting size impression that a ball of Play-Doh exactly 0.869 inch in diameter does not.

You may want to mount the planets on tongue depressors or popsicle sticks so that they are easily used and found. This provides the opportunity to glue the Earth and Moon models on a popsicle stick about 2.4 inches apart.

You can begin the exercise by talking about the planets, their relative sizes, and their distance order from the Sun. It’s fun to have youngsters guess how far apart the planets need to be in the scale model solar system. It’s a good idea to fasten the soccer ball to a traffic sign or a tree so it can be seen as the walk progresses. Another of the million uses for duct tape. Recently, I created photo data tables for each planet, mounted on thin fiberglass rods that can be stuck into the ground. I can discuss with fellow walkers planet vital statistics such as rotation rate, orbital period, atmospheres, and other, sometimes surprising, facts as time and attention allow.

A view from the Earth

A view from the Earth

Walking It Off
The mind-bending part of the planet walk is to pace off the spaces between the model objects. At our scale of 1” = 100,000 mi., the average teenager’s pace (increment the count each time the same foot hits the ground) is about 36 inches, representing the enormous distance of 3,600,000 miles. I assign each planet to a hiker, and have helpers join him in counting abridgment off the paces to the spot where he will place his planet. Walking at a normal speed, we traverse our miniature solar system at the scale speed of 20 times the speed of light (Warp 20)!

After 10 paces, put down Mercury.
Another 9 paces; Venus
Another 7 paces; Earth/Moon

Already, the model is starting to freak people out. Who can believe that our planet can be warmed by something so far (93 million miles / 8 1/3 light-minutes) away? To convince ourselves that the scale is correct we can look back at the soccer ball from Earth’s position and notice (cautiously) that it subtends the same angle as the real Sun in the sky.

Then, the distance intervals increase greatly, astonishment sets in, and grumbling begins in earnest.

Another 95 paces to Jupiter.
Another 112 paces to Saturn.
Another 249 paces to Uranus.
Another 281 paces to Neptune.

When I began doing this exercise with schoolchildren in the 1990’s, I often ended the hike at this point, invoking the convenient excuse that, due to Pluto’s eccentric orbit, Neptune was temporarily the Solar System’s most distant planet. More recently, the IAU’s demotion of Pluto provided a more official abridgment opportunity. Nevertheless, at its furthest extent

Another 242 paces to Pluto.

Extending the Model
If we have the fortitude to complete the model, we will have walked about one thousand yards–about half a mile. To appreciate cosmic distances, that’s just the beginning. Using the scale 1” = 100,000 mi.:

  • 1 AU: 78 feet
  • Extent of Kuiper Belt (30 – 50 AU): ~0.7 miles
  • Furthest reaches of Oort Cloud (100,000 AU): ~1,800 miles
  • One light-year: 928 miles Distance to nearest star (Proxima Centauri): 4,000 miles
  • Diameter of Milky Way galaxy: 91,000 miles
  • Distance to Andromeda galaxy: 2.3 million miles

At the cosmically modest distance to our nearest galactic neighbor, even the model becomes too large to comprehend.

Limitations of the Model
As with all models, this one helps to visualize some aspects of reality, and misleads in others. Most obviously, the real planets do not line up in a straight line on one side of the Sun as the model would have it. As the planets orbit the Sun, the distance between two planets can be anywhere from the differences of their distances from the Sun to the sum of their distances. Seen from above (north of) the ecliptic plane, the planets excepting Pluto all travel counterclockwise in their approximately circular orbits with periods ranging from about 3 months to 165 years.

The Solar System is not as flat as the model depicts. Pluto, for instance, has an orbit inclined to the ecliptic by around 17 degrees. This means that part of its orbit would 600 feet up in the air, and part would be in a hole that is equally deep.A

Sense of Emptiness
How can galaxies interact gravitationally without stars crashing into each other? This model helps provide the sense of emptiness to help visualize vast star clouds passing through each other. A 100,000 mile-wide disk containing on average soccer ball sized objects spaced 4,000 miles apart begins to seem pretty unsubstantial. Why are dim or distant objects so hard to detect? Why do near-earth objects sneak up on us with some regularity? What are the complications and time scales for sending a robot to Ultima Thule? Anyone experiencing this planet walk has taken a fun and important first step (1,019 paces, actually) towards appreciating these kinds of questions.

Guy Ottewell’s publications are available at

Posted in April 2019, Sidereal Times | Tagged | Leave a comment

The weight of Water

by Theodore R. Frimet

The Weight of Water

fundy tides, tidal friction, and Einstein

I ordered a copy of the Observer’s Handbook 2019, back a few months ago. I was pretty stoked that The Royal Astronomical Society of Canada (RASC) had produced its first USA Edition, ever. However, I did it on the cheap, and thanks to a fellow UACNJ member, we ordered a few at a savings. The money saved, however, translated into weeks doing without the guide. I was in no hurry to “jump” to Jenny Jump to pick up my just rewards. My copy lay dormant in the club library, for weeks on end.

The night before I started out for a volunteer site at Blairstown Library, for Makers’ Day, I spied last years 2018 Handbook on the kitchen table. Woa is to me! The 2018 edition would not have the many tidbits of data to answer the many, and exhausting questions that the little tykes would brew up for this amateur. What to do? Put the angst, and anxiety to the side.

I settled into Makers Day. Hundreds passed me by, to visit the arrangement of tables and projects. Many to make granola, or to be wowed by the aluminum 1950’s weavers station. However, I was not even bested by the laser cutter being demonstrated, that day. Proud to be an Amateur Astronomer, I report back to you that not less than 15 adults, and 30 plus children stopped by our wee little habitat.

I be armed with a 12 inch Dobsonian, 6 inch Celestron Newtonian, and 8 inch SCT, books, charts, and binoculars. Hands on for all-comers, all-ages. No exceptions! We had a variety of experiences. They ranged from the youngest trying out the old dob as a merry-go-round, to the many gilded faces looking down at young Newts’ mirrors.

The best personal experiences, however, were in the free books being handed out. They were the former pride and joy of a former Astro-Physicist, turned fusion laser tokamak researcher, now one year retired. And many of his former books hit their mark. Two tomes,which were written in Russian, found their way into a second generation American home, where Mom spoke English as a second language. And yes, Russian was her first. She was stunned how I knew intuitively that the family spoke Russian, and that the boys were so happy. She asked me how I knew? Did I know Russian? I said, “dasvidaniya”. She said, “ok”. I hope I didn’t offend her, as it is probably the ONLY Russian phrase or word that I can passably speak. She smiled. And eventually left the Makers with two happy, and hopefully, future Astro-Physicists in tow.

I look down, now, at the table, and recall why I am writing this essay. The weight of water. I began reading the RASC handbook, yesterday afternoon, while at Jenny Jump. I felt it was a decent way to pass the time, after Makers Day. I curiously turned the page to the ever present article written by Roy Bishop. It is titled, “Tides and the Earth-Moon System”. Roy, unfortunately, writes a little on the long side. He must be a relation of mine, as some of his sentences exceed 50 words, or more. Very tough on the fore-brain. And ultimately, this information is quick to be brain dumped into the sump that holds the overflow of water. Wait. Read that back. Count the words. 19 words. Two more than would be necessary to make a simple sentence incoherent and impossible to absorb. I give pause to my ill gotten comments. Mr. Bishop, I apologize to thee.

Janet cautioned me not to be unruly. In my own experience, I have seen that the pot need not call the kettle black. I reap what I sow. Karma is king. Someone call my editor and complain. Ok. Let’s move on, now.

What you will read is part one of three. And I will not offer you parts two, or three. You can get that from the RASC Observers Handbook 2019, pps 179-183, courtesy Roy Bishop. If you dare. Well, in my Dale Carnegie training, this is called ‘throwing out the gauntlet’. Or is that me smacking you with a glove? I forget. You would do well in heeding my advice. Buy a copy of the USA Edition, RASC Observer’s Handbook 2019. Every Amateur Astronomer, should have a copy at the ready.

The moon exerts Newtonian gravitational forces onto our Earth. The wet part of our world, that is closer to the moon, accelerates towards the moon. That force is greater than the force that accelerates our world, below the water. Yup. You read that right. That creates a bulge of water, that faces the moon.

There is another bulge. It is on the “far side” of the Earth. That is the Earths face that is farthest from the moon. That gets less force. It is almost as if that water is being left behind. Wait a minute. It is being left behind! It bulges out, behind the Earth.

Recap. There are two bulges. One out front of the Earth, facing the moon. And another, lagging behind the Earth, farthest from the moon.

And get this. The Earth rotates below the bulge. So the tide ebbs and flows over the Earth, as the Earth goes about its daily 24 hour rotation. I think that this might explain why closed salt water seas and fresh water lakes do not have “tides” like rivers and oceans. You can comment, here, if you like. Pause. I look up at the ceiling. I am seeing if any of this is sticking. Yes. There it is.

Old Sol also exerts a gravitational force on the Earth. This too affects the tidal forces. Since the Sun is so much farther away than the moon, this force is much less. Yup. Even though the Sun is so massive, it still has a far weaker affect on tides. Distance is everything, now-a-days. The force is counted as the square, and sometimes, in variations, as the cube of the distance. (argh – cubes, squared, pi-rrr-squared!)

But get this. The two tidal patterns (the sun’s and the moon’s) aren’t happening at the same time. At least not always. And when they DO synchronize, we have even higher tides! Happy is the amateur that understands the weight of water. Go now and do our bidding, and pass the good word that centrifugal force is a myth, and that water weighs in. Newton would be proud.

There is much more. Fundy Tides. Tidal Friction (my favorite). And General Relativity and Tides. However, I want you to have access to the indisputable facts and figures from the handbook. And if I’ve whetted your whistle, me thinks that you will be reading from the latest edition in no time, soon. Thank you, Editor James S. Edgar, for bringing us the Observers Handbook 2019, USA Edition.

Author side note: “if you appreciate gravitational forces on our earth, then it is not a quick leap of faith, in your understanding, and in our mentoring path, to comprehend that there are many tidal forces in the universe; always playing a role in the compaction and distortion in the play-dough like consistency of minor and major planetary bodies, stellar bodies, and yes, dare I say it, ever eerily to speak its name. Yes, black holes.” Oops. Word count = 70. Very weighty.

Posted in April 2019, Sidereal Times | Tagged | Leave a comment

How vast is our Solar system ?

How vast is our solar system ? We know that the Sun is at the center of the solar system. How far does it extend ? The outer edge of the solar system has been extending since the ancient times to today. There is no unambiguous and precise definition of the outer edge. There are couple of considerations we can look at. Let us start with what the solar system consist of.

Firstly, the solar system has planets orbiting around the Sun. There are eight of them in all. Starting from Mercury to Neptune. Each of the planets have their own moons which circle them. While the smaller ones may have one or two moons, the bigger planets have several of them. The distances in our solar system are not measured in miles or kilometers. Instead we use AU (Astronomical Unit). 1 AU is the distance from the Sun to the Earth (about 93 million miles or 150 million kilometers). Once we go beyond our solar system, we use light years or parsecs to measure distances across other stars and galaxies.

The four inner planets – namely Mercury, Venus, Earth, Mars – are all rocky planets. They are comparatively close to each other and to the Sun as well. They are all solid by and large and have a very thin gaseous atmosphere. Next we have the asteroid belt which contains a large number of small objects, essentially made of minerals and ores. These are perceived to be remnants from the formation of our solar system about five billion years ago. Like the rubble left after constructing a building. The garbage was thrown just a few blocks from the backyard !

Next four planets are the outer gaseous giants – namely Jupiter, Saturn, Uranus, Neptune. They are much larger than the inner rocky planets. And they consist largely of gases with a very small solid core at the center. And the distance increases as we go towards the outer fringes of the solar system. Saturn is at 10 AUs from the Sun. Similarly, Uranus is at 20 and Neptune at 30 AUs. It is like the stations on a railway line coming at increasing distances as we go away from a city.

Planets up to Saturn were known to our ancients as they are visible to the naked eye. Uranus had to wait till the invention of the telescope, to be discovered. Neptune was predicted theoretically based on mathematical calculations of gravitational tug on Uranus and other planets. And later observed through a telescope, thus validating the prediction.

As we find the limit of the solar system is extending, the cold body called Pluto was discovered and accorded the status of a planet. In the last decade, hundreds of such bodies, some of them larger than Pluto were found. Pluto, at a distance of 40 AUs from the Sun, was demoted to be a dwarf planet or a planetesimal. All these cold bodies were found to be part of a region named as the Kuiper belt, named for the astronomer Gerard Kuiper, extending from 40 to 60 AUs. We found a new suburb of our solar system, again presumably the remnants of the formation of our solar system !

The NASA spacecraft Voyager 1, which was launched in 1977 on a mission to visit the outer planets, has gone past the Kuiper belt. Now It is at a distance of 140 AUs from the Sun. This is considered as beyond the edge of the solar system, as per one definition.

The Sun gives out energetic particles called the solar wind. They travel very quickly at the speed of the light and encounter a similar wind which is known as inter-stellar wind, which blows between the stars. This wind is more of a radiation than a wind we normally know on the Earth. With the inter-stellar wind, space is not truly empty. At about 95 AUs, the solar wind slows down and becomes hotter. This region is called the termination shock. At about 125 AUs, the influence of the solar wind wanes and the inter-stellar wind takes over. This is the edge of the solar system, as per the realm of the solar wind.

There is a second consideration of how much gravitational influence the Sun has. There are comets, which are largely icy bodies with tails, which can be observed from time to time with a naked eye. Some of these comets come from the outer parts of the solar system. They are in an elongated orbit and come closer to the Sun once in a hundred years or so. They are predicted to be formed in a region called the Oort cloud, named for a Danish astronomer Jan Oort. This region is a spherical region enveloping our solar system, unlike the planets and the asteroid and the Kuiper belts which are all roughly on a single plane. And the Oort region is at a whopping distance of fifty thousand AUs ! Yet, the Sun has a gravitational influence over the objects in this region. Hence, this can be considered as the outer limit of the solar system.

But the problem is that Oort cloud has not been observed using any telescope. Presumably due to the small size of the objects scattered in a vast region. It is just a prediction shared by the community of astronomers. Someday we might be able to photograph the Oort cloud. As per the distance of the Oort cloud, Voyager at just 140 AUs has long long way to go to be considered as away from home.

Editors’ note: Please check a related article on this topic titled “The Earth as a Peppercorn” by Victor Davis.

Posted in April 2019, Sidereal Times | Tagged | Leave a comment


compiled by Arlene & David Kaplan



Planet Jupiter: Spectacular picture of Jupiter’s storms
This beautiful picture of Jupiter was assembled from three separate images acquired by Nasa’s Juno spacecraft as it made another of its close passes of the gas giant…more



Exoplanet tally set to pass 4,000 mark
The number of planets detected around other stars – or exoplanets – is set to hit the 4,000 mark…more

Posted in April 2019, Sidereal Times | Tagged , | Leave a comment